I thought of this, too. Isn't there a movie that shows that a cop's standard procedure when dealing with demands is to slow things down and get the perp talking? The intelligent perp (per Hollywood) then kills someone to let the police he's serious.
In addition, his choice of locale & victim could be interpreted a responding directly to Moose.
I have changed back from terrorist, to nut job thinking along these lines. I think this guy is a hard boiled fiction fan, not a foreign nut, or a military, or right wing type.
Cat and mouse games. Ransom demands with voice scrambler, playing around with the cops, killing an FBI agent... this is a game. I bet once this person is found, you will find their house full of books by Cornwell, Deaver, Patterson, and Kellerman. This guy is a nut who thinks (maybe rightly so), that he is as smart as the killers in all his favorite police procedural novels, and is doing this as his great statement to the world, that he isn't a bookish, dateless, friendless nerd, but that he is important.
I could be wrong. For over a week, I thought terrorist, but now with the risky behaviour, ransom, calling cards, taunting notes, voice changer, etc... it does sound to me like a person playing out crime novels for real.